RAX-A compact instrument for Raman Spectroscopy aboard the Phobos rover of the MMX mission

Abstract

The JAXA "Martian Moon Exploration" (MMX) mission to Phobos will include a small rover (see presentation S. Ulamec) which carries the Raman Spectrometer for MMX "RAX". The instrument is compact and lightweight yet sensitive enough to allow precision measurements of the mineralogical composition of Phobos' surface material. Here we describe the preliminary system design of the RAX spectrometer and its performance goals. It consists of an external compact laser source, fiber coupled to a spectrometer and a focusing unit as well as ancillary systems. The laser source for the spectrometer has been developed by INTA/Universidad de Valladolid for the Raman Laser Spectrometer (RLS) onboard ESAs Exomars Rover. The highly miniaturised RAX Spectrometer module (RSM) is a new development by DLR which contains a multi-objective optical system and space qualified detector and is optimized for size and performance. The focusing unit from JAXA/University of Tokyo provides finely resolved open-loop focusing over a 15 mm stroke. The entire RSM has a mass of less than 1.4 kg and a volume of only 81 x 98 x 125 mm³. RAX will be operated with the rover in-the-loop. Thus automated focusing, measurement and in-situ data processing will allow autonomous Raman spectra measurements of regolith to be taken at various sites of interest on Phobos (see presentation S. Routley). These measurements will be validated against measurements on Earth and Raman-spectra libraries. An in-flight verification is used for instrument calibration after launch. The data obtained will be compared with the Raman spectra from the ExoMars2020 mission on the Martian surface and thus support determining the origin of Phobos.